We've camped at Sands of Time RV in Avon.
http://www.sandsoftimecampground.com/
It is a passport America and the rate is $20.00.
57 Total RV sites (15 tent). Full hookups, water electric (20/30/50 amp service), sewer, can accommodate RV’s up to 40 ft, 30 x 50 minimum campsite size, laundry, cable TV, hot showers, and horseshoes. Two bedroom, fully furnished cottages including A/C and cable TV. Park is conveniently located to beach, wind-surfing, fishing pier, restaurants. Located 35 miles from Nag’s Head and Manteo, and 6 miles from Buxton.
We only stayed a few days but found it convenient.
By the way, we entered from the North and exited the islands to the south via the 3 hour ferry ride.
Enjoy it.